1. Field of the Invention
This invention relates to a copper alloy material and a method for producing the same.
2. Description of the Related Art
As a material for constituting conductors of equipment cables or contact wires for feeding rail vehicles, a copper material is used. This copper material is required to have not only a high electrical conductivity, but also a high mechanical strength from the point of view of bending properties and wear resistance.
In view of the foregoing, as a copper material for contact wires, a copper alloy material which is produced by alloying copper (Cu) with magnesium (Mg) for example is used. The copper alloy material including the magnesium is superior in mechanical strength as well as electrical conductivity because of solid solution strengthening resulting from the magnesium forming a solid solution in a copper parent phase.
The copper alloy material including the magnesium is produced by, for example, melting a copper parent material into a molten copper, thereafter adding, fusing magnesium to the molten copper, and casting a molten copper alloy including the magnesium. In general, copper alloy materials are produced in the form of long wire rods by a continuous process throughout from casting to rolling using an SCR (Southwire Continuous Rod) system, etc.
Because magnesium is an easily oxidizable metal element, the production of the copper alloy material has the following drawback: The easily oxidizable magnesium, when added to the molten copper, is oxidized due to oxygen that is included in the molten copper to form a magnesium oxide (e.g. MgO). The magnesium oxide remains solid without being fused to the molten copper because of its higher melting point than the molten copper temperature. In other words, some of the magnesium added remains in the form of its oxide without being fused to the molten copper. As a result, the copper alloy material produced by the casting contains a smaller amount of solid solution of the magnesium formed in the copper parent phase than the additive amount of the magnesium added when produced, and no sufficient solid solution strengthening by the magnesium results. In this manner, since some of the magnesium is not fused to the molten copper due to being oxidized, its addition yield is low and no desired solid solution strengthening is likely to result.
In view of the foregoing, as a method for suppressing the oxidation of the magnesium to be added to the molten copper, JP Patent No. 5515313 for example has suggested a method by deoxidizing the molten copper before adding the magnesium to the molten copper. Specifically, the oxygen amount included in the molten copper is reduced by deoxidization to not larger than 10 ppm, followed by adding the magnesium to the molten copper. This allows the fusion of the magnesium to the molten copper while suppressing the oxidation of the magnesium in the molten copper. Please see e.g. JP Patent No. 5515313.